Phosphotriesterase (PTE) is an enzyme found in soil bacteria which degrades organophosphorus compounds, mainly synthetic insecticides. It appears to be an evolutionary anomaly in that although the only known substrates for PTE are synthetic and have only been in existence for about 50 years, the enzyme has already evolved itself to maximum catalytic efficiency. I am attempting to further characterize the enzyme to see if it has an endogenous function, since it seems highly unlikely that PTE would have maximized its efficiency in only 50 years. As a step in the characterization process, I will be making a model of PTE based on crystal coordinates of the apoenzyme (without its two catalytic divalent metal ions) to see if I can get any insight. The crystal structure of the holoenzyme has just been solved as well; and I plan to model that once the coordinates are in the database. Comparisons between the structures of the holoenzyme and apoenzyme can then be made. Furthermore, a gene downstream of the PTE gene has recently been discovered to have high sequence homology to the PTE gene itself; it could possibly be an evolutionary precursor. The crystal structure of this protein has not been attempted yet; but once it has been completed, a long term goal of the project will be to model that as well and compare the active sites and general scaffolding of PTE and the homologue utilizing the facilities of the Computer Graphics Lab.